There are typically three tuning technologies used in an external cavity tunable laser: 1) tuning is achieved by using a precision stepping motor to drive a grating to rotate, and this technology has the following shortcomings: first, there are quite high requirements on stepping moving precision and repeatability of the stepping motor in achieving precision optical frequency tuning, thus the cost is relatively high; second, the purpose of miniaturization is hardly achieved due to the stepping motor used; and third, the operational stability is poor under a harsh working environment, in particular, resistances to various mechanical vibrations are poor. Because of these problems, the tunable laser using this technology is only suitable for use under a laboratory working environment; 2) tuning is achieved by a tunable acousto-optic filter. This technology has the advantages of high tuning speed, no mechanical moving component and small size. However, it has the shortcomings of low tuning precision and relatively wide filtering bandwidth, therefore, the tunable laser using this technology is only suitable for applications in which both the tuning precision and the output bandwidth are not high; and 3) tuning is based upon the temperature-sensitive characteristics of the transmission optical frequency of grating or other optical filtering devices in laser resonant cavity, such as an optical Etalon. This tuning technology has high tuning precision and relatively narrow spectrum bandwidth, but low tuning speed. Therefore it is not suitable when the wide spectral range tuning is needed, for example: if the temperature coefficient of an optical filtering device is 0.02 nanometers/degree, the desired spectrum range and temperature adjustment range are 20 nanometers and 100 degrees respectively, which is impracticable for some applications.